In a projection-type video image display apparatus projecting video image onto a screen or the like (hereinafter, referred to as a “projector” in some cases), a white light source such as a high pressure mercury lamp or a xenon lamp has been conventionally used mainly as a light source. However, from a perspective of heat generation, product life, and resistance to obstacles, a light emitting diode (LED) light source has been recently used. In this case, for example, light sources of three colors such as red (R), green (G), and blue (B) are independently provided, and light rays emitted from these light sources are mixed and synthesized to form white light.
Meanwhile, in a conventional technique, when change such as reduction of quantity of light caused by degradation of a light source and temperature characteristics may be generated, in order to maintain desired preferable white light, quantity of light (illuminance) of light emitted from the light source is measured by a sensor provided in a projector or the like, and the measured value is fed back to output control of the light source to adjust the quantity of light.
For example, Japanese Patent No. 4559949 (Patent Document 1) describes an apparatus including a light source having emitting elements with different colors, and an optic element (prism) having a reflective material provided on a front surface thereof, the optic element being positioned to receive and reflect light emitted from the light source, in which a plurality of photosensors each measuring light having a different wavelength are mounted over a portion of the front surface of the optic element on which the reflective material is not provided, of the front surface of the optic element on which the reflective material is provided, and in which a control system receives measurement values from the plurality of photosensors to separately adjust light output of each of the emitting elements of the light source in accordance with the received measurement values.